Impact of active dose management on radiation exposure and image quality in computed tomography: An observational study in 1315 patients

[Restructuring Torso CT Protocol for Radiation Dose Management]

PURPOSE

There are problems with dose management in X-ray computed tomography (CT) because the protocol used for any examination is not always in the same scan range. The purpose of this study was to investigate the usefulness of setting the CT protocol based on the scan range.

METHODS

We evaluated the examination data of patients who underwent plain CT based on a scan range of chest to pelvis and abdomen to pelvis. The previous protocol [Chest-Abdomen Routine] was changed to the current protocols [Chest_Abdomen] and [Chest_Pelvis], and the previous protocol of [Abdomen Routine] was changed to the current protocols [Abdomen] and [Abdomen_Pelvis]. Examination data of height, scan length, volume CT dose index (CTDI_vol), and dose length product (DLP) were obtained from digital imaging and communications in medicine, and radiation dose structured report using Radimetrics. The relationship between patient height and scan range, and CTDI_vol and DLP was indicated in a scatter plot. Standard deviation (SD) of scan length and DLP were compared between current and previous protocols. Outliers were defined as the data exceeding average ±2SD.

RESULTS

The SD of scan length decreased by 77.1% on abdomen to pelvis, and the SD of DLP decreased by 65.2% on abdomen to pelvis. The causes of the outliers were CT scan range, scan parameter, arm position, metal implants, and body thickness of patients.

CONCLUSION

Setting CT protocols based on the scan range reduced SD of scan length and DLP. It was helpful for reducing the number of scan range outliers and analyzing the cause of outliers.

CT dose management of adult patients with unknown body weight using an effective diameter

PURPOSE

To assess the usefulness of effective diameter (D_eff) for CT dose management of adult patients with unknown body weight.

METHODS

A total of 642 adult patients whose height and weight had been measured before CT examination (chest CT using Aquilion Prime SP, 428 patients; chest CT using Biograph mCT, 100 patients; and abdominal CT using Aquilion Prime SP, 114 patients) were retrospectively examined between April 2018 and September 2019. The D_eff was automatically calculated from the lateral diameter on a CT localizer radiograph by a dose management software (Radimetrics). In order to determine the correlation between body weight and D_eff, we compared volume CT dose index and dose length product between patients with body weight between 50 and 70 kg and those with D_eff equivalent to body weight between 50 and 70 kg. Correlation analysis was performed by Pearson's product-moment correlation, and statistical analyses were performed by using t-test.

RESULTS

The correlation coefficient values between body weight and D_eff were 0.920 for chest CT using Aquilion Prime SP, 0.929 for chest CT using Biograph mCT, and 0.805 for abdominal CT using Aquilion Prime SP. In both chest and abdominal CT scans, there were no significant differences in volume CT dose index and dose length product between patients with body weight between 50 and 70 kg and those with D_eff equivalent to body weight between 50 and 70 kg.

CONCLUSIONS

The D_eff may be useful as a somatometric parameter for CT dose management of adult patients with unknown body weight.